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Pentel raised the possibility that a vaccine could be used in conjunction with the drug Zyban, which has demonstrated clinical effectiveness in helping smokers stop.

"The vaccine does not cross-react with [Zyban]," Malin tells WebMD. "The hope is that the vaccine would make smoking ineffective -- people wouldn't get anything from smoking -- while [Zyban] might reduce the longer-term craving." But, he adds, "Whether it would work out that way remains to be seen."

The safety of the vaccine is another unknown. Pentel tells WebMD, "It needs some more safety testing, and we're doing that."

An additional question is whether the vaccine would lose its power if individuals using it smoked in sufficiently heavy quantities. "That, in my mind, is the most serious concern," Malin tells WebMD. "It's being intensively investigated right now."

Pentel noted that scientists examined a heroin vaccine in the 1970s, but gave up over the concern that heavy use of the drug would overwhelm the vaccine. All the same, he said, this issue may be solvable -- a cocaine vaccine has overcome this concern and is now in clinical trials.

According to Malin, Pentel's work "has shown that you can have repeated administration of nicotine beyond levels that ordinarily smokers would have without saturating the vaccine. It is difficult in the rats to saturate the vaccine." Nevertheless, he says, "It's going to be one of the key issues in human trials. When people try to smoke more to overcome the [nicotine] blockade, do they succeed or fail?"

As a final issue, Pentel acknowledged that the nicotine vaccine might potentially block nicotine analogues from being effective. Nicotine analogues are substances that are clinically similar to the drug that scientists believe may have therapeutic effects against Tourette's syndrome and other nervous system problems.

Would the vaccine make an individual "immune" to these potential therapies? According to Malin, "The answer is probably not, because these [nicotine] antibodies are very selective so far. But you would have to check that one by one with each potential therapy."